1. Field of the Invention
The present invention generally relates to a loudspeaker horn, and, more specifically, to a loudspeaker horn having a constant directivity over a wide frequency range.
2. Description of the Prior Art
U.S. Pat. No. 4,187,926 issued to C. A. Henricksen et al. on Feb. 12, 1980, Japanese Patent Public Disclosure No. 6875/82 and C. A. Henricksen et al. "The Manta-Ray Horns", JOURNAL OF THE AUDIO ENGINEERING SOCIETY, September 1978, Volume 26, Number 9, p. 629-634 respectively disclose a horn as shown in FIGS. 1a and 1b. Such a horn has vertical and horizontal side walls which have linear configurations expressed by such equations as y=ax+b. This type of horn has the advantage of an easily controlled directivity angle, but has the disadvantage that radiation characteristics in a low frequency range of the horn become distorted because the cross-sectional area of the horn resembles a conical horn.
Japanese Patent Public Disclosure No. 76995/82 discloses a horn as shown in FIGS. 2a and 2b. The side wall of such a horn is expressed by y=a.sub.0 (1+.alpha.x).sup.n, where n assumes n.sub.1 (&gt;2) at the side of the horn aperture and n.sub.2 (&gt;n.sub.1) at the side of throat. This type of horn is advantageous in that radiation characteristics in a low frequency range are less distorted since the side wall of the horn is formed by two kinds of Besser functions and the cross-sectional area of the horn extends near exponentially. On the other hand, this type of horn has a disadvantage in that it is difficult to control its directivity angle because the included angle of the horn starts to change from the throat end and there is an uncertainty as to where the two curves should best intersect.
Japanese Patent Public Disclosure No. 212198/86 discloses another type of horn as shown in FIG. 3. Such a horn has side walls each formed in an arc. This results in a near exponential rate of increase in cross section and produces good radiation characteristics in a low frequency range of the horn, but does not provide any solution for the control of the directivity angle of the horn.